50.1 Plant containment will be provided to limit radioactivity release to the environ­ment. This release will not exceed the limits described in 10 CFR 20 for normal opera­tions and for transient situations which might be expected to occur, and 10 CFR 100 for potential accidents which have a very low probability of occurrence.

50.2 This inner containment structure will be designed to withstand peak pressures and temperatures above those which could occur as a result of the design basis accident, taking into account the calculational uncertainties. The structure will be designed to P, psig excess pressure associated with a maximum temperature of 7i°F at the liner, but not necessarily simultaneously.

50.3 The design basis accident for the inner containment will be the worst credible core disruptive accident.

50.4 The reactor inner containment structure atmosphere will be at all times inerted with a maximum oxygen content of 2%. A sodium fire will be deemed to be incredible within the reactor containment structure.

50.5 The reactor inner containment structure will be designed to have a leakage rate of less than Lj v/0 per day+ even under the design peak pressures and temperatures.

50.6 The outer containment building will be designed to withstand peak pressures and temperatures above those which could occur as a result of its design basis accident, taking into account the calculational uncertainties. The building will be designed to P2 psig excess pressure associated with a surface temperature of T2°F.

50.7 The design basis sodium fire for this outer containment building will be that associated with a sodium pool in an open IXH vessel.

50.8 The outer containment building will be designed to have a leakage rate of less than L2 v/0 per day even under the design peak pressures and temperatures.

50.9 The design will preclude open interconnection between the atmosphere of the inner containment structure and the atmosphere of the outer containment building unless the sodium temperature in the primary circuit has been reduced to below 300°F.

50.10 Primary coolant components of the IHXs and pumps will be drained of primary coolant before the components are removed to maintenance areas.

50.11 The design of both containment buildings will accommodate earthquake load­ings and other environmental loadings that the site might make necessary, in addition to normal static loads.

The design pressures and temperatures P1,P2,T1, T2 and leakages Lx, L2 are set with suitable margins from the safety evaluation of certain design basis accidents as outlined in Section 5.4.

Within these still fairly wide rules the designers’ codes and standards must set the methods and define the numerical limitations within which he works to meet the criteria. There may be a number of design methods of meeting the leakage limitations set by 50.5 for example, even at the condi­tions specified in 50.2 to restrict the choice. Ultimately there are other criteria that also come into play in the final choice of solution, the most important being the cost. The designer has many masters to satisfy, and he uses the criteria as guide lines in his work.